1. Field
One embodiment of the present invention relates to a disk drive device provided with a disk media and a head positioning control method applied to the disk drive device.
2. Description of the Related Art
Generally, in a disk drive device typified by a hard disk drive (sometimes simply referred to as disk drive), a servo pattern (servo data) is written on a disk media which is of a recording media. The servo pattern is used to perform head positioning control. In the disk drive, a head is positioned at a target position (target track) on the disk media using the servo pattern read by the head.
Usually, the servo pattern written on the disk media includes plural radial servo patterns (sometimes also referred to as servo wedge). The plural radial servo patterns are used to define plural concentric tracks on the disk media. The radial servo pattern is written on the disk media through a servo writing process included in a disk drive production process.
Recently, there is proposed a method, in the servo writing process, plural spiral servo patterns (sometimes referred to as spiral tracks) which become a base pattern (seed pattern) are written on the disk media and the radial servo patterns are written based on the plural spiral servo patterns (for example, see U.S. Pat. No. 7,248,426 B1).
In such cases, the radial servo pattern is a servo pattern (product servo pattern) which is used during an actual operation in the disk drive shipped as a product. Accordingly, finally each spiral servo pattern is deleted from the disk media by overwrite.
In the servo writing process, the disk media in which the plural spiral servo patterns are recorded is usually incorporated in the disk drive. The plural radial servo patterns (product servo pattern) are written on the disk media by a self-servo writing process performed by the disk drive.
In writing the radial servo pattern, a read head reads the plural spiral servo patterns to obtain a detection signal. The disk drive computes a position error to perform head positioning control based on the detection signal. The disk drive usually includes a head called an integrated head. A read head which reads the servo pattern and data and a write head which writes the servo pattern and data are mounted on the integrated head while the read head separated from each other. A width of the read head is relatively narrower than a width of the write head. This leads to generation of a signal having a particular shape, specifically a hexagonal shape in the detection signal of the spiral servo pattern read by the read head.
In the position error computation method adopted to perform the head positioning control, there is well known a position error computation algorithm for the radial servo pattern. Servo burst signals A, B, C, and D are used in the position error computation algorithm. The position error computation method is an algorithm which enables the head position error to be computed with sufficient accuracy. However, the detection signal obtained by reading the plural spiral servo patterns is different from the servo burst signals A, B, C, and D. Accordingly, it is difficult that the detection signal is directly used in the position error computation algorithm.
Therefore, it is necessary to realize a new function of being able to position the head with sufficient accuracy using the detection signal obtained by reading the plural spiral servo patterns.